The present invention relates to a tapered roller bearing of the type defined in the preamble to claim 1.
Conventionally, as illustrated in attached FIG. 1 which is a partial axial section of a roller bearing of known type, each of the two radially inner half-races 10 is formed with a step 11 close to the inner end which faces towards the centre of the bearing. This step serves, during the transfer stages which precede assembly of the sub units comprising the sets of rollers 12 and associated cages 13 on respective inner half-races, and before insertion of these sub-units into the outer race 14, to prevent the rollers from accidentally escaping from the rolling tracks in the direction indicated by the arrows A and Axe2x80x2 in FIG. 1.
The formation of the above-mentioned step involves a first disadvantage in that its shape, projecting radially from the rolling plane of the rollers, requires the provision of excess metal of a significant thickness t on the forged blank race, the outline of which is indicated in broken outline in FIG. 2. Moreover, it takes a long time for the significant mass of material constituting the excess metal to be removed by turning and grinding operations (proportional to the quantity of excess metal to be removed); in addition, the weight of the forged blank is detrimentally effected by the excess metal part. This known technique is therefore disadvantageous from a productive point of view, relating both to the working time taken for finishing and the weight of the component, which detrimentally influences the transfer operations.
The said step involves a second disadvantage in that, to complete an inner half-race, the sub-unit comprising the preliminarily assembled rollers in their cage must be fitted onto the half-race by passing them over the step; this subunit is assembled by pressing the rollers and the cage in the opposite directions from those indicated by the arrows A and Axe2x80x2 in FIG. 1.
In the formation of the half-races by stamping elements obtained from bar stock, it is advantageous if the shape which is impressed in the stamping phase of the forging corresponds substantially to the shape of the finished product which is obtained subsequently by working, that is turning and grinding, the blank workpiece. As can be observed from FIG. 2, the presence of the step makes the conical surfaces C and Cxe2x80x2 of the stamped blank and the finished piece respectively are not parallel. In the grinding operation, therefore, a surface (Cxe2x80x2) is formed which is orientated differently from the surface (C) which was formed by stamping.
Whilst it is not desired to be bound to any theory in this connection, the Applicant has reason to believe that it would better exploit the structural strength of the half-races if the form impressed by the stamp were to correspond to the shape which it will have during use supporting a load. In other words, a greater strength would be obtained, and consequently a longer useful life for the bearing if the said conical surfaces were parallel.
Referring again to FIG. 1, the inner cylindrical surface of the half-races is further worked in such a way as to form retaining grooves 16 for a temporary retainer ring 17, usually of plastics or metal. This, by holding the two inner half-races together axially, prevents each of them from accidentally slipping out from the outer ring 14, thus preventing escape of the rollers. This arrangement, while being effective, is expensive in that it requires the formation of the temporary retainer ring 17xe2x80x94which once the bearing is assembled, loses its functionxe2x80x94and in that it is also necessary to form the said retainer grooves 16.
An object of the present invention is to provide a tapered roller bearing in which the radially inner races do not have the conventional step discussed above, so as to avoid the above-indicated disadvantages.
Another object of the invention is to provide a bearing which does not need the conventional temporary retainer ring, and avoids the disadvantages associated therewith.
This and other objects which will become better understood hereinafter, are achieved in accordance with the present invention by a bearing having the characteristics set out in claim 1.
Other important characteristics are set out in the dependent claims.
Further characteristics and advantages of the invention will become clearer from the detailed description of an embodiment thereof, with reference to the attached drawings, given purely by way of non-limitative example, in which:
FIG. 1 is a partial axial section of a prior art tapered roller bearing;
FIG. 2 is a partial axial section of an inner half-race formed according to the prior art;
FIG. 3 is a partial axial section of a tapered roller bearing according to the present invention; and
FIG. 4 is a partial axial section of an inner half-race for the bearing of FIG. 3.